1. Technical Field
The present invention relates to a liquid crystal display apparatus and a method for restraining a bright point, and in particular, relates to a liquid crystal display apparatus to make the bright point which is generated due to a tiny foreign material unnoticeable and a method for making the bright point unnoticeable.
2. Background Art
In recent years, there is an increasing demand for enhancing quality of a liquid crystal display apparatus which uses TFT (Thin Film Transistor) as a switching element. Among of the increasing demands for enhancing quality, one of the most noticeable quality degradation is a bright point. The bright point is a light leakage point which is visible at a state that an image in half-tone or black is displayed. The bright point whose width is about several tens μm is mainly generated due to a tiny foreign material which is mingled in an assembly process of the liquid crystal display apparatus and whose width is about several μm to several tens μm or the like.
In the liquid crystal display apparatus in normally black mode, a light leakage due to refraction by the foreign material which is mingled in the assembly process of the apparatus or one due to disturbance of orientation of its liquid crystal by the foreign material is always visible as the bright point.
In case that the liquid crystal display apparatus is applied to a home television set, a PC monitoring device or the like, the bright point with the very small size which is several % of size of a unit pixel or a dot which composes an image has not been regarded as a defective indication.
However, in case that it is applied to a high quality display, for instance, a medical monitoring device, the bright point is regarded as a defective indication even if its size is tiny. The reason is that a distance between user and the apparatus is short and a minute and subtle image is read from a gradation display when it is applied to the medical monitoring device.
Furthermore, a brightness of transmitted light in a monochromatic liquid crystal display apparatus is high, while that in a color liquid crystal display apparatus is attenuated by a color filter and is not so high. Therefore, when the monochromatic liquid crystal display apparatus is applied to a high quality display, the bright point is noticeable and is regarded as a defective indication.
Here, in a TFT liquid crystal display apparatus, there is a defective indication that not a part of the dot but a whole area of the dot is defective. A main reason for the defective indication in the whole area of the dot is a defective patterning which is generated in a manufacturing process of a TFT substrate.
A method to restore the defective patterning of TFT has been already established almost perfectly. Generally, the defective patterning is destroyed by applying a laser beam, and consequently, the operation of TFT is normalized. Or, a pixel electrode and a constant voltage signal electrode are short-circuited and connected each other by applying the laser beam, voltage of the pixel electrode is fixed to the constant voltage, and consequently, the operation of TFT is normalized
On the contrary, at the present time when there is no method for removing the foreign material, there is no effective method to restore the bright point due to the tiny foreign material or the like.
For example, when the laser beam is applied to the foreign material, it is almost impossible to destroy it perfectly. Even if the foreign material is destroyed, its broken pieces may scatter into a normal area, and consequently, the area having the bright point may rather become wide.
Here, a patent document 1 (Japanese Patent Publication No. 3565327) discloses a technology related to a method for restraining a defective dot. The patent document 1 discloses a technology that makes the defective dot, which is always in a black state and whose whole area can not be controlled electrically, unnoticeable. That is, a signal applied to dots whose number is n (integer which is not smaller than 1) and which are adjacent to the defective dot is controlled, and a total brightness of n of the dots is controlled to be approximately equal to original brightness of the defective dot.
FIG. 9 is a top view showing a state around a defective dot of a liquid crystal display apparatus disclosed in the patent document 1. In FIG. 9, a dot 12 is the defective dot. The defective dot 12 is always in the black state and cannot light even when a whole should light actually. Accordingly, the brightness of a dot 13 and a dot 14, which are adjacent to the defective dot 12, are controlled to make a state of a brightness generated if the dot 12 can light, and consequently, an influence of the defect is reduced visually.